In a mouse model of silica induced pulmonary inflammation and fibrosis developed in this laboratory, silica exposure increases expression of ICAM-1 on lung (alveolar~interstitial) macrophages and type II epithelial cells. By understanding the role and regulation of silica induced ICAM-1 expression in lung macrophages, it may be possible to modulate its expression, alter leukocyte trafficking and suppress lung injury. Using murine macrophages in vitro, this proposal will test the following hypothesis: Silica induced ICAM-1 expression in lung macrophages participates as a signal transduction molecule and is regulated, in part, by cytokines (TNFalpha, Il-1beta, IFNgamma) released in response to silica exposure. Specific Aim I:. To test the hypothesis that silica induced ICAM-1 expression participates in the ability of silica exposed murine macrophages to generate critical inflammatory mediators involved in particle induced pulmonary inflammation. Mouse macrophages (primary culture, a cell line) will be stimulated in vitro with silica particles to increase ICAM 1 expression. ICAM-1 -mediated signal transduction will then be activated either by the addition of rat anti-mouse ICAM antibody and a cross linking antibody or by co-culture with MAC-1 positive peritoneal PMNS. Products of this activation [cytokine (TNFalpha, IL-1beta, IFNgamma) release, reactive oxygen species and nitric oxide, ICAM-1 protein expression, transcription factor (NFkB, AP-1) activation] will be measured. Specific Aim 2: To test the hypothesis that TNFalpha, IL-1beta, IFNgamma) participate in silica induced ICAM-1 expression. Mouse macrophages (primary culture, cell line) will be activated in vitro with silica particles and ICAM-1 protein expression, mRNA levels and promoter activation will be measured in the presence or absence of specific anti-cytokine antibodies. Mouse macrophages will also be exposed to these cytokines (individually or in combination) in the absence of silica to determine if these mediators will elicit ICAM-1 expression.